Method and means for operating electric motors



Oct. 8, 1929. s. G. NOTTAGE METHOD AND MEANS FOR OPERATING ELECTRICMOTORS Filed April 25, '192s /lxCLsL WV TORNE iNvENTOF 57am/@y /Vo #ageWITNESSESZ 542/ fm@ Patented Oct. 8, 1929 UNITED STATES PATENT- OFFICESTANLEY G, NTAGE, F MURRAYSVILLE, PENNSYLVANIA, ASSIGNOR TG WESTING-HOUSE ELENBRIC t MANUFACTQRIHG COMFANY, A CGRPGEATION OF PENNSYL- VANAAND KMS FCL-R- @PERATNQ ELECTRIC MGIRS Application led pril QS,

My invention relates to a method of, and means for, operating aplurality of electric motors, and it is particularly applicable to theoperation of a plurality of series-Wound motors of the colnmutator type.

In railway service, alternating-current motors of the series-Woundcommutator type are commonly employed because of their characteristic ofdeveloping a large starting torque, 16 which is necessary in this classofservice. Motors of this type do not conimutate well when starting froma source of alternating current. This is because an inducedelectronxotive force is produced in that portion of the larmatureWinding between tWo consecutive cornznutator segments, While it isshort-circuited b the brushes; This induced electromotive "cree cannotbe vreadily compensated for at starting.

object of my invention is to provide a method of, and means for,operating such serieawound commutator type motors whereby they maydevelop a large starting torque with good commutation.

practicin my invention, 1 employ mothat may e operated either fromdirect rent or from alternating current, such, example, as series motorsof the commuor type.

l operate such a motor by initially supplydirect current to it forstarting, and by applying both direct current and alternating currentduring a portion, at least, of its acceleration. A motor of the seriestype starts under such conditions as a direct current motor and producesa large starting torque Without ditliculty in commutation. After themotor is started, it will operate satisfactorily by applyin both directcurrent and alternating 0 current uring the acceleration period.

In practicing my invention, I also employ a lll novel arrangement ofmotor circuits.

rality of motors are connected in parallel-circuit relation and to asource of direct current for initially starting the motors as direct.

1926. Serial No. itl/A092,

current motors., Thereafter, a source of alternating current isconnected Vto substantially equipotential points of said circuits withreference to the direct-current source, the directcurrent source beingconnected to substantially equipotential points of the circuits withreference to the alternating-current source.

In operating a plurality of motors connected in parallel-circuitrelation as above described, it may happen that the points chosen asequipotential points with respect to the direct-current andalternating-current circuits vary slightly from the true equipotentialpoints on account of different counterelectromotive forces of theseveral machines, and also on account of dissimilar characteristics ofthe magnetic circuits of the machines during the two half cycles of thealternatingcurrent Wave. To overcome this objection, I propose toconnect an equalizing transformer in the circuit, at the junction of theconnection to the source of alternating current and the loop circuitthrough the motors, thus preventing the alternating current from fiowingthrough the direct-current source.

Another object of my invention is, therefore, to provide means forequalizing the voltage drop through the several portions of the parallelcircuits and for prevent-ing the flow of alternating current through thedirect-current source.

My invention will be better understood by reference to the accompanyingdrawing in which,

Fig. 1 is a diagrammatic View of circuits vand apparatus, including anequalizing transformer, embodying the principles of my-invention,showing the circuits as they exist at starting.

Fig. 2 is a View of a similar system, with the circuits as they existduring the accelerating and running operations of the motors;

Fig. 8 illusf'srar detail of the windings of the equalizing transformerillustrated schematically in Figs. l and 2.

Referring to Fig. 1 of the drawing, a plurality of motors 1,2, 3 and 4are provided, cach having commutator-type armature windings 5, 6, 7 and8 and series wound field windings 9, 10, l1 and 12. rIlle motors 1, 2, 3and 4 are connected in a loop circuit by means of conductors 13, 14, 15and 16. A source of direct-current power, such as a generator 17, isconnected to the motor circuits at midpoints 18 and 19, thus forming twosubstantially similar loop circuitsthrough the niotors 1 and 3, and themotors 2 and 4, respectively. The generator 17 may be connected to ordisconnected froln, the motor circuits by means of switches 21 and 22.source of alternating-current power, such as a transformer 23, ymay beconnected to the motor circuits at points 24 and 25 (respectivelyintermediate motors 1 and 3, and motors 2 and 4) by means of switches 2Gand 27.

The direct-current generator 17 comprises an armature winding 28, ashunt field windl ing 29, and an adjustable rheostat 31 for varying theenergization of the lield winding to control the voltage of thegenerator. y

rlhe alternating-current source of supply comprises the transformer 23having aprimary winding 32 that is connected between a trolley wire 33and ground 34, andasecondary winding 35 that is connected by means orconductors 36 and 37, through switches 26 and 27, respectively, to thepoints 24 and 25 of the motor circuit. As illustrated, the secondarywinding 35 of the transformer 23 is provided with a series of taps, forproducing a variation of the applied alternating-current voltage byvarying the point of connection of the conductor 37 to the winding 35.

When it is desired to start the motors, the switches 21 and 22 are irstclosed, thus connecting the several motors to the direct-currentgenerator 17, as. illustrated in Fig. 1. After the motors have beensuitably started, the switches 26 and 27 are closed andalternating-current is applied, the circuit arrangement beingillustrated in Fig. 2. The eld rheostat 3l of the direct-currentgenerator 17 may then be adjusted to increase the voltage of thedirect-current that is applied to the motors. The point of connection ofthe conductor 37 to the secondary winding 35 of the alternating-currenttransformer 23 may also be varied to increase the voltage of thealternating current that is applied to the motors. After the directcurrent voltage has been increased to a given value, the motors may beaccelerated by control of the alternating current voltage, preferablyWithout any further increase in the direct current voltage. When themotors have accelerated sutiiciently, the switches 21 and 22 are opened,the switches 21 and 22, in their open positions, being illustrated bybroken lines the circuits of the sysacross it diagonally, that is, tothe points 18' and 19, and the alternating current source 23 beingconnected to the alternate diagonal points, that is, to points 24 andDirect current from the source 17 will, therefore, flow Vthrough theloop circuit comprising Inotors 1 and 3 and through the loop circuitcom- 'prising motors 2 and 4, the two-loop circuits being connected inparallel relation to each other.

Current from the alternating current source 23 will flow through the twoparallel circuits comprising motors 1 and 2, and motors 3 and 4,respectively. It will also be apparent that points 18 and 19 aresubstantially equipotential points with respect to thealternatingcurrentfcircuits and that points 24 and 25 are substantiallyequipotential points with respect to the direct-current circuits.

Should the voltage drops of the alternatingcurrent circuits be somewhatunequal, so that the points 18 and 19 are not exact equipotentialpoints, the alternating current will tend to flow through thedirect-current generator 17. To prevent or oppose such current flow,

an equalizing transformer 38 illustrated in Fig. 3 is provided. Theequalizing transformer 38 is provided with three windings 41, 42 and 43,upon a magnetizable core 44. The windings 41 and 42, which aredifferentially related and have an equal number of turns located on eachside of the mid-point 19,

are so connected that the alternating current through the motors 3 and 4traverses these windings in a direction such that the fluxes producedthereby act to neutralize each other. The winding 43 may be connectedtothe generator armature 28 through the switch 22 and to the mid-point19 located between the windings 41 and 42. Winding 43 comprises a numberof turns that is equal to the number of turns of each of the windings 41and 42. Since the direction of direct current flowing in the coil 41 isopposite to that iowing in the coil 42, and since these two coils aredifferentially wound, the fluxes produced by these two coils, by theflow of direct current. will be cumulative and will be opposite to, andneutralized by, the flux produced inthe coil 43. In other words, theampere-,turns of coil 43 are equal to the ampere-turns of coils 41 and42 combined, since all three coils have the same number of turns and thecurrent of coil 43 is the sum of the currents of the coils 41 and 42.

.1V hen the alternating current flowing through the'motors 3 and 4passes through the windings 41 and 42 of the equalizing FAB transformerwithout passing through the coil 43, the system is ina condition ofbalance. Should, however, a portion of the alternating current passthrough the coil 43 and the generator 17, the coil 43 would produce aflux that is unn'eutralized by the flux created by current in the coils41 and 42, and the alternating-current iuXes in the coils 41 and 42would become unequal, thereby failing to neutralize cach other. Theeffect of this unbalanced condition of the windings 41 and 42 would beto produce a counter-electromotive force in the winding 43 that opposesthe sage ot alternating current through the Winding and thedirect-current generator 1'4".

Various incdiiications may be circuits and apparatus disclosed plicationwithout departing freni t" my invention, and I do not wish to be'limited other than by the scope of the appended claims,

I claim as my invention:

1. In combination, a source of alternating current, a source of directcurrent, a plurality ot series commutator motors connected in parallelcircuits, means for connecting said source of directcurrentto saidmotors, means for connecting said source of alternating currentto saidmotors at substantially equipotential points of said circuits withreference -to the direct current source, said direct current sourcebeing connected at substantially equipotential points of said circuitswith reference to the alternating current source, and means forequalizing the potential drop through the circuits included between saidseveral equipotential points to oppose the flow of alternating currentto said direct current source.

2. In combination, a source of alternating` current, a source ofdirectcurrent, a plurality ot series commutator motors connected inparallel circuits, means for connecting said source of direct current tosaid motors, means for connecting said source of alternating current tosaid motors at substantiallyequipotential points' of said circuits withreference to the direct current source, said direct current source beingconnected at substantially equipotential points of said circuits withreference to the alternating current source, and means for equalizingthe potential drop between said several points comprising a magnetizablecore, two differentially related coils wound upon said core andconnected in series circuit relation between two of said motors, and athird coil wound upon said core and connected in series circuit relationwith said source of direct current.

3. In combination, a source of alternating current, a source of directcurrent, a plurality ot' series commutator motors interconnected andarranged as a Wheatstone bridge, one motor being connected in each ofthe respective branches constituting said bridge, means In testimonywhereof, I have hereunto subscribed my name this 14th day of April,1926.

STANLEY G. NGT

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